>addon domain

Do you mean a sub domain?

No, an addon domain. I have a main domain and an additional domain on the same hosting. They are separate domains and separate site, but use the same space hosting i have buy

do both domains serve all the content or are they kept separate?

@phranque I don't know if I understood your question correctly, but the contents of the two sites (two domains) are different and they will not link to each other

Are you planning to redirect the contents of the old subdomain to the new separate domain? If they were previously indexed under the old domain's URL like https://example.com/subdirectory/page.html and now will have URLs like https://example.com/page.html using the new domain then you should want any old links to redirect (301) to their new domain's URLs. It makes a difference if they were never crawled or indexed. But if Google has ever seen them - then it becomes important.

A new, separate domain can be set up to appear to be a separately hosted domain.

@not2easy The contents of the subdirectory have already been largely deindexed. All the contents of the subdirectory will be transferred to the addon domain, but will be published gradually as I update them and with a new title and url. Do any of you here use addon domains? I've already done a search but the information I found is all very old. I wouldn't want to have problems with seo

CPanel offers an easy how-to - assuming your host uses CPanel. I used this setup about 18 years ago and I messed it up so I learned how to do it a step at a time. I just looked it up, this is from 2012, but updated in 2018 and it looks like it is still good: https://cpanel.net/blog/tips-and-tricks/managing-multiple-domains-from-a-single-cpanel-account/

While I'm sure there are steps somewhere here on the forums, I can't find anything with our current search setup. Others here might know where that information is locally.

Yes, I have hosting with cpanel. Thanks for the link. I also found a video of Matt Cutts but he was very old, although he says that there are no problems, I don't know if anything has changed in recent years with addon domains and seo